A wide variety of food products have one or more portions that are bonded together. For example, numerous Ready-To-Eat ("R-T-E") or breakfast cereals and snack pieces are in the form of biscuits having an upper and a lower layer. The biscuits can include a center filling, e.g., a fruit paste, or be unfilled. The finished biscuits can be prepared by finish baking, puffing, or other finish drying step, of a cereal pellet or snack half product fabricated having upper and lower layers. These pellets can be fabricated by crimp cutting individual pieces from, for example, two layered cooked dough sheets or continuous dough ribbons fed to a two roller, counter rotating crimp cutter (see, for example, U.S. Pat. No. 5,217,739 entitled Methods For Flipping And Aligning A Dough Sheet issued Jun. 8, 1993). The crimp cutter not only forms a mechanically created seal or bond between the dough layers but also sections the dough sheets into individual pieces. (See also commonly assigned U.S. Ser. No. 014,919 filed Feb. 8, 1993 entitled Device For Crimping and Cutting Dough Ropes which describes a high speed apparatus.)
In another example, two layers of farinaceous doughs for a pizza crust are mechanically bonded together by a docking method which forms numerous pinch bonds or docking points between the dough layers. The docked two dough layers can be deep fat fried to provide a product exhibiting greater crispness upon subsequent oven baking.
While such apparatus and techniques are useful, there can be problems with such methods particularly concerning the strength or integrity of the seal or bond between the food layers formed by conventional mechanical methods.
One problem is that the composition of food layers to be mechanically bonded are limited in composition. High fat levels in the layer materials must be avoided since fat levels in the composition adversely affect seal integrity or bond strength. Also, the moisture content must be carefully controlled. If a cooked cereal dough is too wet, the dough can be sticky and hard to work with. If too dry, while easily handled, the dough may fail to form a seam.
Another problem involves the integrity of the seal or bond especially particularly if there is an intermediate layer, e.g., a fruit paste or a fat based filling. The presence of an intermediate layer, especially when fat based, increases the likelihood that the seal will have imperfections or discontinuities. Forming a continuous seal is even more difficult if either of the cereal dough layers has a high fat and/or moisture content. Breaches in the seal or bond between the outer dough layers can result in leakage of the filling. Filling leakage, of course, is highly undesirable leading not only to diminished consumer acceptance but also to significant manufacturing inconveniences.
Still another problem involves maintaining the bond during subsequent processing. For example, many snack half products are deep fat fried to provide finished products, especially puffed products. Mechanically formed bonds or sealing seams often cannot endure the rigors of deep fat frying especially if fabricated from doughs that expand upon deep fat frying. While this problem is particularly severe in deep fat frying, the problem can also arise in other puffing methods, e.g., fluidized bed hot air heating which can also be used for both finish drying and puffing.
Surprisingly, ultrasonic energy has now been found to be useful in forming a bond or acoustic weld or seal between food layers such as in a laminated cereal pellet for an R-T-E or snack biscuit. The ultrasonic energy can be used in substitution for mechanical compression crimping or docking techniques.
Ultrasonic apparatus and techniques are well known and are commonly employed in a variety of areas, especially in the plastics industry. However, it has been surprisingly discovered that ultrasonic energy can be used in connection with cereal dough processing to realize improved cereal products and methods.
More surprisingly, the bonds or acoustic welds formed in the present food products are remarkably robust. As a result, a wide variety of new and appealing R-T-E cereal or snack shapes or other food pieces can now be created characterized by having at least one acoustic weld between the layers.
Another surprising advantage of the present invention is that employment of ultrasonic energy allows for greater freedom in food layer and filling composition since ultrasonic welding is more tolerant of food composition and condition.
Still another surprising aspect of the present invention is the provision of a bond between two food layers essentially characterized in having a tensile strength to the bond greater than the tensile strength of the materials being bonded. Such an improved strength bond is not believed possible to form using conventional mechanical crimping techniques.